A burnable gas containing hydrogen and/or carbon monoxide or a fuel that can be fed to a fuel cell for generating electric current can be produced from a fuel commonly used to operate motor vehicles, for example, diesel fuel, biodiesel, gasoline or synthetic fuels, by the fuel being subjected to a reforming process.
A corresponding fuel treatment device usually has for this a mixture formation space for evaporating the fuel into a homogeneous reaction mixture in the gaseous or vapor form. The mixture formation space is designed, furthermore, to form a so-called “cold flame,” in which a partial oxidation of the fuel takes place in a first process step. The fuel treatment device contains, furthermore, a reaction space with a catalyst designed, for example, as a coated monolith, or reformer, in which further conversion of the reaction mixture into reaction products, such as CO, H2, CO2, N2 and H2O, takes place.
Since the fuels used in motor vehicles contain, as a rule, a certain percentage of sulfur, the fuel treatment device is equipped, in addition, with desulfurization device or a desulfurization stage in order to counteract poisoning of the fuel cell or of the reformer by sulfur. Desulfurization of the fuel may be carried out, in principle, in front of the fuel treatment device, by desulfurization of the reaction mixture after the processing in the mixture formation space or by desulfurization of the synthesis gas after the reformer.
The above-mentioned assembly units of the fuel treatment device are usually designed as separate units, which are connected to one another via flow ducts. This is especially true of the desulfurization stages commonly used in the state of the art, because these are designed as replaceable components. This embodiment of a desulfurization device (stage) is represented, for example, by cartridges, which are filled with a carrier material consisting of a sulfur-adsorbing material, such as zinc oxide. If the absorption capacity of the zinc oxide for sulfur is reached, these desulfurization stages must be replaced with new ones, and they are therefore integrated in the fuel treatment device, as a rule, such that they are readily accessible and can be easily replaced.
Such a fuel treatment device is known, for example, from the document EP 1 735 081 B1. The drawback of the above-mentioned design is, however, that heat exchange can take place among the individual assembly units to a very limited extent only. Furthermore, fuel treatment devices of this design turn out to be relatively large and therefore also heavy, which is undesirable in light of the limited availability of useful space in mobile systems and leads, moreover, to a sluggish warm-up characteristic of the fuel treatment device.
Since each of the above-mentioned assembly units has an activation or working temperature, which is far above the ambient temperatures occurring (approximately 350° to) 950°), an external preheater is necessary for each of the assembly units at least during a restart of a fuel treatment device cooled to the ambient temperature. This causes, besides a considerable extra design effort, an additional installation volume as well as higher costs of the fuel treatment device.